装卸作业的类别分为()。
A.装货卸货作业
B.搬运移送作业
C.放置取出作业
D.配货作业
E.安置保管
参考答案:A, B, C, D
The secretary worked all night long, ______ a long speech for the president.
[ ]
A. to prepare
B. preparing
C. prepared
D. was preparing
在金属构架上高处作业的照明电源电压不大于36V。()